Troubleshooting Active Directory Replication

Selecting a preferred bridgehead server, and other solutions to poor performance in Active Directory replication.

 By Brien M. Posey
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In the first three parts of this series, I explained the importance and techniques of breaking large organizations into sites for the purpose of Active Directory replication. As you've no doubt learned, a considerable amount of planning should go into dividing your network, because doing so can be complicated. As with any complicated process, things can and sometimes do go wrong. In this article, I'll discuss some techniques that you can use to troubleshoot Active Directory replication.

Choosing a Preferred Bridgehead Server

If replication seems slow, you can compensate by creating a preferred bridgehead server within each site. A bridgehead server is the replication point in each site. For example, if a site has four domain controllers, you don't want all four to try to replicate their individual copies of the Active Directory information to a foreign site. Doing so would result in excessive network traffic, because every domain controller in the organization would try to replicate its information to and from every other domain controller.

Instead of using such a chaotic technique, one domain controller in each site acts as a spokesman for all other domain controllers within the site. This domain controller is known as the bridgehead server. If a domain controller other than the bridgehead server needs to distribute Active Directory updates, it does so only within the local site. After the domain controllers within the site have been updated, the bridgehead server then replicates the changed information to the other sites. Only the bridgehead server can make contact with the other sites in the organization.

By the nature of the site structure, each site is automatically set up with a bridgehead server. However, the bridgehead server that Windows 2000 selects may not always be the best choice. Because it must handle all replication-related traffic and functions in addition to its normal workload, carefully consider which server should act as the bridgehead server in each site.

Ideally, the bridgehead server should have a relatively light workload and lots of bandwidth to spare. As long as the bridgehead server has plenty of processing power, memory, hard disk space, and bandwidth, the replication requests will be handled quickly and efficiently.

You can specify more than one preferred bridgehead server. Only one server in each site can actually function as the bridgehead server, but if you've listed multiple servers as preferred bridgehead servers, Windows 2000 will select the bridgehead server based on preference starting with the first server on the list. Should the first server on the list of preferred bridgehead servers fail, the second server on the list will be used. If all the servers on the list fail, or if you don't have any servers on the list, Windows 2000 will automatically designate one domain controller in each site as a bridgehead server.

To designate your preferred bridgehead server, follow these steps:

  1. Click Start and choose Programs|Administrative Tools|Active Directory Sites and Services.

  2. In the AD Sites and Services console, navigate through the tree and select the domain controller you want to make into the bridgehead server. Right-click on the server and select Properties from the resulting context menu.

  3. In the server's properties sheet, you'll see a list of transports available for directory replication. Select the transport protocol of choice and click Add. The transport protocol will move from its original location to the area that designates the server as a preferred bridgehead server for the listed protocols.

This article was originally published on Oct 30, 2000
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